The present invention is related to extrudable black body decoy flare compositions that dramatically improve processibility while maintaining the infrared radiation intensity of conventional decoy flare compositions. More particularly, the present invention is related to such compositions that are also capable of serving as a heat-seeking missile decoys for aircraft, tanks, and trucks.
Aircraft-launched flares of various types have been used for many purposes. For example, it is often desirable to light a particular area at night. A flare may be used to produce light for search and rescue operations or for various military purposes. It is also well known to employ flares as a decoy tactic. That is, a flare may be used to cover the path of an aircraft through a particular area. One common situation is when the aircraft is encountering anti-aircraft fire. The use of a flare can distract the anti-aircraft fire sufficiently to allow the aircraft to proceed safely on its course.
Anti-aircraft missiles are commonly used in modern warfare. Such missiles may be launched from the ground or they may be launched from another aircraft. Many of this type of missile are designed to seek particular types of emissions characteristic of aircraft. Such emissions often take the form of heat and infrared light. Thus, xe2x80x9cheat-seekingxe2x80x9d missiles are often used against aircraft.
In this context, it is desirable to provide a flare that produces the type of emissions sought by the missile in older to distract the missile from the actual aircraft. Thus, flares that emit heat and infrared are well known and have been used for many years.
Conventional decoy flare materials have been a combination of magnesium and polytetrafluoroethylene (PTFE or xe2x80x9cTeflon(copyright)xe2x80x9d) These compositions are known widely as magnesium-Teflon(copyright) flare compositions. These formulations produce a black body emission spectrum which has been used as a decoy for jet engines.
Current methods of producing magnesium-PTFE flare compositions require the use of solvents that are ozone-depleting or flammable. In one currently used method, the composition is produced by depositing the binder on the pyrotechnic mixture through solvent loss using, for example, acetone or methyl-ethyl ketone. The mixture is dried, after which it is consolidated through pressing or extrusion operations. In a second method, a binder such as Viton A(copyright), which is a fluorinated ethylene propylene copolymer sold by DuPont, is deposited on the pyrotechnic mixture through polymer precipitation methods using hexane and acetone. The dried pyrotechnic powder is then consolidated through pressing or extrusion operations. This method requires large quantities of acetone and hexane, which are flammable, to carry the Viton A(copyright) binder. The solvents used in these methods have been the source of many fires during the processing of decoy mixes.
An additional problem with conventional magnesium-PTFE compositions is that they are very sensitive. Moreover, such compositions require extensive operator exposure during mixer dumping, oven loading, and material break-up operations. Traditional methods have proven disadvantageous, as the processing and handling of conventional flare compositions is dangerous and has resulted in many injuries and even deaths. An additional problem with conventional magnesium-PTFE compositions is that such compositions typically require expensive ingredients such as specialty binders and spherical magnesium.
Accordingly, it would be a significant advancement in the art to provide compositions and methods of producing decoy flares that overcame the identified problems of producing conventional flares. In particular, it would be an advancement to provide flare compositions that eliminate the safety risks associated with handling unconsolidated pyrotechnic powder. It would also be an advancement in the art to provide flare compositions and methods of production that eliminate ozone-depleting or flammable solvent emissions that accompany production. It would be a further advancement in the art to provide such flare compositions that could be manufactured using traditional press/extrusion techniques or using a twin screw extruder.
It would also be an advancement to provide such compositions that exceed the radiometric performance of conventional magnesium-PTFE infrared decoy flare compositions. It would be a further advancement in the art to provide such compositions that cost less than conventional flare compositions to produce.
Such compositions and methods for producing decoy flares are disclosed and claimed herein.
The present invention is related to new compositions that produce black body radiation when ignited. A black body radiator is generally defined as a material that radiates over a broad spectrum, as described by the following equation:
xe2x80x83M=xcex5"sgr"T4 W cm.2
where:
xcex5=emissivity
T=absolute temperature
"sgr"=Stefan-Boltzmann constant
M=exitance
The novel extrudable black body decoy flare compositions defined herein function in a manner similar to conventional magnesium-PTFE infrared decoy flares: heat produced by the flare decoys the heat-seeking missile away from the target. The principle difference between a conventional magnesium-PTFE flare composition and this new flare composition is that the compositions of the present invention utilize polyaromatic thermoplastics rather than solvent deposition fluor-polymers (e.g., Viton A(copyright)) or poly-olefins as the binder component. The polyaromatic thermoplastic facilitates the processing of the flare material via extrusion without the use of solvents.
The primary reaction products of a conventional magnesium-PTFE flare are solid carbon and liquid magnesium fluoride. The high emissivities of these reaction products result in an efficient black body radiating plume. In contrast, the polyaromatic thermoplastic of the present invention pyrolyzes during flare combustion to produce carbon particles. This pyrolysis of the binder results in an efficient black body radiator in the exhaust plume.
The present invention relates to the use of polyaromatic thermoplastic compounds such as polystyrene and dimethyl phthalate as the binder in a black body decoy flare. The thermoplastic compounds enable a magnesium-PTFE flare composition to be extruded without the use of solvents. In addition, the aromatic rings are reduced to carbon in the fuel rich composition, producing an ideal incandescent species that augments the signature.
Pyrotechnic art teaches that the radiometric output of traditional flare formulations is directly tied to the binder content of the flare. Low binder levels (4%) produce the greatest radiometric output and high binder levels (8%) produce lower radiometric output. One traditional method for augmenting the radiometric output of a flare formulation when higher binder levels are required is to use a fluorocarbon (such as Viton A(copyright)) or high energy binder (e.g., a polyoxetane binder such as BAMO/AMMO). This increases the oxidative potential of the binder component. Therefore, it was unexpected that high polyaromatic binder (16%) content flares produced an increased output when compared to a standard maoncsium-PTFE flare.
Some of the primary benefits of the present invention are enhanced processibility, increased performance, elimination of solvents, and reduction in material and labor costs. Extrusion of flares containing polyaromatic thermoplastic binders increases processibility over traditional pressed flares by eliminating oven cure time, increasing processing line speed, decreasing labor costs, and significantly reducing the risk to operators from unconsolidated pyrotechnic exposure. The radiometric output of the flare is improved over traditional pressed magnesium-PTFE flares. The use of thermoplastic binders eliminates the need to use solvents to process the flare compositions. The solvents traditionally used are ozone-depleting or flammable. Elimination of solvents increases the environmental friendliness of the process and safety to operators. Polyaromatic thermoplastics are commonly used in the manufacture of a wide variety of products ranging from coffee cups to children""s toys. These materials are far less expensive than halocarbons such as Viton A(copyright) or specialty binders commonly used in the manufacture of infrared flares.
Flares manufactured using compositions of the present invention are more easily demilitarized than flares manufactured using conventional compositions. Compositions utilizing polyaromatic thermoplastic binders may be removed from the flare casing by heating. This is to be contrasted with conventional flare materials which can be demilitarized only by complex and expensive mechanical or chemical processes.
These and other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.